Ultrahigh-temperature ceramics (UHTCs) have a unique combination of high melting points, high strengths, and high chemical stabilities, which makes them unique materials for a wide range of ultrahigh-temperature (> 2000 °C) applications. Herein, we first report a novel highly porous dual-phase high-entropy UHTCs material composed of a high-entropy boride (HEB) phase and a high-entropy carbide (HEC) phase, which was fabricated via foam-gelcasting-freeze drying technology and high-temperature sintering with mixed borides and carbides as raw materials. The as-fabricated samples have a uniform pore structure and a firm skeleton that consists of random alternating distributions of HEB and HEC particles. The porous dual-phase high-entropy UHTCs samples have ultrahigh porosities of 96.4%–90.1%, low densities of 0.31–0.87 g/cm³, high strengths of 0.45–4.17 MPa and low thermal conductivities of 0.202–0.281 W/(m·K), as well as better oxidation resistance than single-phase HEC. The present results highlight the potential of as-prepared porous dual-phase high-entropy UHTCs as promising materials for ultrahigh-temperature thermal insulation applications.